As electric vehicle are getting more and more popular, the performance of a transmission is getting more and more important. Most of existing electric vehicles adopt one-speed transmission with a constant gear ratio of 6.4:1˜7.5:1. Under such circumstance, when the vehicle is driving up the slope, the one-speed transmission cannot provide a high torque; and when the vehicle is driving on a flat road, the one-speed transmission cannot provide a high speed due to the restriction of the transmission gear ratio.
Since existing one-speed transmissions cannot be effectively used, many problems will arise. For example, the climbing capability is poor, the start-up is energy consuming, and the efficiency is low. When the vehicle is driving down the slope and the speed is accelerated, the electric motor may be dragged, and to the worse, may even be burnt down.